Predefined ColorSchemes

- added support for predefined color schemes
- moved all the code regarding colors generation from wallpaper to the
ColorSchemes service

Assets/ColorSchemes/Nord.json

@@ -0,0 +1,19 @@
+{
+    "mPrimary": "#8fbcbb",
+    "mOnPrimary": "#2e3440",
+    "mSecondary": "#88c0d0",
+    "mOnSecondary": "#2e3440",
+    "mTertiary": "#5e81ac",
+    "mOnTertiary": "#2e3440",
+
+    "mError": "#bf616a",
+    "mOnError": "#2e3440",
+
+    "mSurface": "#2e3440",
+    "mOnSurface": "#d8dee9",
+    "mSurfaceVariant": "#3b4252",
+    "mOnSurfaceVariant": "#e5e9f0",
+    "mOutline": "#434c5e",
+    "mOutlineVariant": "#4c566a",
+    "mShadow": "#2e3440"
+}